/*
 * Copyright 2010 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.zxing.aztec.decoder;

import com.google.zxing.FormatException;
import com.google.zxing.aztec.AztecDetectorResult;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.common.DecoderResult;
import com.google.zxing.common.reedsolomon.GenericGF;
import com.google.zxing.common.reedsolomon.ReedSolomonDecoder;
import com.google.zxing.common.reedsolomon.ReedSolomonException;

import java.util.Arrays;

/**
 * <p>The main class which implements Aztec Code decoding -- as opposed to locating and extracting
 * the Aztec Code from an image.</p>
 *
 * @author David Olivier
 */
public final class Decoder {

  private enum Table {
    UPPER,
    LOWER,
    MIXED,
    DIGIT,
    PUNCT,
    BINARY
  }

  private static final String[] UPPER_TABLE = {
      "CTRL_PS", " ", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P",
      "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "CTRL_LL", "CTRL_ML", "CTRL_DL", "CTRL_BS"
  };

  private static final String[] LOWER_TABLE = {
      "CTRL_PS", " ", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p",
      "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "CTRL_US", "CTRL_ML", "CTRL_DL", "CTRL_BS"
  };

  private static final String[] MIXED_TABLE = {
      "CTRL_PS", " ", "\1", "\2", "\3", "\4", "\5", "\6", "\7", "\b", "\t", "\n",
      "\13", "\f", "\r", "\33", "\34", "\35", "\36", "\37", "@", "\\", "^", "_",
      "`", "|", "~", "\177", "CTRL_LL", "CTRL_UL", "CTRL_PL", "CTRL_BS"
  };

  private static final String[] PUNCT_TABLE = {
      "", "\r", "\r\n", ". ", ", ", ": ", "!", "\"", "#", "$", "%", "&", "'", "(", ")",
      "*", "+", ",", "-", ".", "/", ":", ";", "<", "=", ">", "?", "[", "]", "{", "}", "CTRL_UL"
  };

  private static final String[] DIGIT_TABLE = {
      "CTRL_PS", " ", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", ",", ".", "CTRL_UL", "CTRL_US"
  };

  private AztecDetectorResult ddata;

  public DecoderResult decode(AztecDetectorResult detectorResult) throws FormatException {
    ddata = detectorResult;
    BitMatrix matrix = detectorResult.getBits();
    boolean[] rawbits = extractBits(matrix);
    boolean[] correctedBits = correctBits(rawbits);
    String result = getEncodedData(correctedBits);
    return new DecoderResult(null, result, null, null);
  }

  // This method is used for testing the high-level encoder
  public static String highLevelDecode(boolean[] correctedBits) {
    return getEncodedData(correctedBits);
  }

  /**
   * Gets the string encoded in the aztec code bits
   *
   * @return the decoded string
   */
  private static String getEncodedData(boolean[] correctedBits) {
    int endIndex = correctedBits.length;
    Table latchTable = Table.UPPER; // table most recently latched to
    Table shiftTable = Table.UPPER; // table to use for the next read
    StringBuilder result = new StringBuilder(20);
    int index = 0;
    while (index < endIndex) {
      if (shiftTable == Table.BINARY) {
        if (endIndex - index < 5) {
          break;
        }
        int length = readCode(correctedBits, index, 5);
        index += 5;
        if (length == 0) {
          if (endIndex - index < 11) {
            break;
          }
          length = readCode(correctedBits, index, 11) + 31;
          index += 11;
        }
        for (int charCount = 0; charCount < length; charCount++) {
          if (endIndex - index < 8) {
            index = endIndex;  // Force outer loop to exit
            break;
          }
          int code = readCode(correctedBits, index, 8);
          result.append((char) code);
          index += 8;
        }
        // Go back to whatever mode we had been in
        shiftTable = latchTable;
      } else {
        int size = shiftTable == Table.DIGIT ? 4 : 5;
        if (endIndex - index < size) {
          break;
        }
        int code = readCode(correctedBits, index, size);
        index += size;
        String str = getCharacter(shiftTable, code);
        if (str.startsWith("CTRL_")) {
          // Table changes
          shiftTable = getTable(str.charAt(5));
          if (str.charAt(6) == 'L') {
            latchTable = shiftTable;
          }
        } else {
          result.append(str);
          // Go back to whatever mode we had been in
          shiftTable = latchTable;
        }
      }
    }
    return result.toString();
  }

  /**
   * gets the table corresponding to the char passed
   */
  private static Table getTable(char t) {
    switch (t) {
      case 'L':
        return Table.LOWER;
      case 'P':
        return Table.PUNCT;
      case 'M':
        return Table.MIXED;
      case 'D':
        return Table.DIGIT;
      case 'B':
        return Table.BINARY;
      case 'U':
      default:
        return Table.UPPER;
    }
  }

  /**
   * Gets the character (or string) corresponding to the passed code in the given table
   *
   * @param table the table used
   * @param code the code of the character
   */
  private static String getCharacter(Table table, int code) {
    switch (table) {
      case UPPER:
        return UPPER_TABLE[code];
      case LOWER:
        return LOWER_TABLE[code];
      case MIXED:
        return MIXED_TABLE[code];
      case PUNCT:
        return PUNCT_TABLE[code];
      case DIGIT:
        return DIGIT_TABLE[code];
      default:
        // Should not reach here.
        throw new IllegalStateException("Bad table");
    }
  }

  /**
   * <p>Performs RS error correction on an array of bits.</p>
   *
   * @return the corrected array
   * @throws com.google.zxing.FormatException if the input contains too many errors
   */
  private boolean[] correctBits(boolean[] rawbits) throws FormatException {
    GenericGF gf;
    int codewordSize;

    if (ddata.getNbLayers() <= 2) {
      codewordSize = 6;
      gf = GenericGF.AZTEC_DATA_6;
    } else if (ddata.getNbLayers() <= 8) {
      codewordSize = 8;
      gf = GenericGF.AZTEC_DATA_8;
    } else if (ddata.getNbLayers() <= 22) {
      codewordSize = 10;
      gf = GenericGF.AZTEC_DATA_10;
    } else {
      codewordSize = 12;
      gf = GenericGF.AZTEC_DATA_12;
    }

    int numDataCodewords = ddata.getNbDatablocks();
    int numCodewords = rawbits.length / codewordSize;
    if (numCodewords < numDataCodewords) {
      throw FormatException.getFormatInstance();
    }
    int offset = rawbits.length % codewordSize;
    int numECCodewords = numCodewords - numDataCodewords;

    int[] dataWords = new int[numCodewords];
    for (int i = 0; i < numCodewords; i++, offset += codewordSize) {
      dataWords[i] = readCode(rawbits, offset, codewordSize);
    }

    try {
      ReedSolomonDecoder rsDecoder = new ReedSolomonDecoder(gf);
      rsDecoder.decode(dataWords, numECCodewords);
    } catch (ReedSolomonException ex) {
      throw FormatException.getFormatInstance(ex);
    }

    // Now perform the unstuffing operation.
    // First, count how many bits are going to be thrown out as stuffing
    int mask = (1 << codewordSize) - 1;
    int stuffedBits = 0;
    for (int i = 0; i < numDataCodewords; i++) {
      int dataWord = dataWords[i];
      if (dataWord == 0 || dataWord == mask) {
        throw FormatException.getFormatInstance();
      } else if (dataWord == 1 || dataWord == mask - 1) {
        stuffedBits++;
      }
    }
    // Now, actually unpack the bits and remove the stuffing
    boolean[] correctedBits = new boolean[numDataCodewords * codewordSize - stuffedBits];
    int index = 0;
    for (int i = 0; i < numDataCodewords; i++) {
      int dataWord = dataWords[i];
      if (dataWord == 1 || dataWord == mask - 1) {
        // next codewordSize-1 bits are all zeros or all ones
        Arrays.fill(correctedBits, index, index + codewordSize - 1, dataWord > 1);
        index += codewordSize - 1;
      } else {
        for (int bit = codewordSize - 1; bit >= 0; --bit) {
          correctedBits[index++] = (dataWord & (1 << bit)) != 0;
        }
      }
    }
    return correctedBits;
  }

  /**
   * Gets the array of bits from an Aztec Code matrix
   *
   * @return the array of bits
   */
  boolean[] extractBits(BitMatrix matrix) {
    boolean compact = ddata.isCompact();
    int layers = ddata.getNbLayers();
    int baseMatrixSize = compact ? 11 + layers * 4 : 14 + layers * 4; // not including alignment lines
    int[] alignmentMap = new int[baseMatrixSize];
    boolean[] rawbits = new boolean[totalBitsInLayer(layers, compact)];

    if (compact) {
      for (int i = 0; i < alignmentMap.length; i++) {
        alignmentMap[i] = i;
      }
    } else {
      int matrixSize = baseMatrixSize + 1 + 2 * ((baseMatrixSize / 2 - 1) / 15);
      int origCenter = baseMatrixSize / 2;
      int center = matrixSize / 2;
      for (int i = 0; i < origCenter; i++) {
        int newOffset = i + i / 15;
        alignmentMap[origCenter - i - 1] = center - newOffset - 1;
        alignmentMap[origCenter + i] = center + newOffset + 1;
      }
    }
    for (int i = 0, rowOffset = 0; i < layers; i++) {
      int rowSize = compact ? (layers - i) * 4 + 9 : (layers - i) * 4 + 12;
      // The top-left most point of this layer is <low, low> (not including alignment lines)
      int low = i * 2;
      // The bottom-right most point of this layer is <high, high> (not including alignment lines)
      int high = baseMatrixSize - 1 - low;
      // We pull bits from the two 2 x rowSize columns and two rowSize x 2 rows
      for (int j = 0; j < rowSize; j++) {
        int columnOffset = j * 2;
        for (int k = 0; k < 2; k++) {
          // left column
          rawbits[rowOffset + columnOffset + k] =
              matrix.get(alignmentMap[low + k], alignmentMap[low + j]);
          // bottom row
          rawbits[rowOffset + 2 * rowSize + columnOffset + k] =
              matrix.get(alignmentMap[low + j], alignmentMap[high - k]);
          // right column
          rawbits[rowOffset + 4 * rowSize + columnOffset + k] =
              matrix.get(alignmentMap[high - k], alignmentMap[high - j]);
          // top row
          rawbits[rowOffset + 6 * rowSize + columnOffset + k] =
              matrix.get(alignmentMap[high - j], alignmentMap[low + k]);
        }
      }
      rowOffset += rowSize * 8;
    }
    return rawbits;
  }

  /**
   * Reads a code of given length and at given index in an array of bits
   */
  private static int readCode(boolean[] rawbits, int startIndex, int length) {
    int res = 0;
    for (int i = startIndex; i < startIndex + length; i++) {
      res <<= 1;
      if (rawbits[i]) {
        res |= 0x01;
      }
    }
    return res;
  }

  private static int totalBitsInLayer(int layers, boolean compact) {
    return ((compact ? 88 : 112) + 16 * layers) * layers;
  }
}
